third rail

The locomotive third-rail pick up shoes are of the new standard S.R. type. … Whenever the locomotive was working hard there was unmistakable evidence of its higher power than its predecessors in the brilliant and explosive arcing between conductor shoes and the third rail; this was particularly vivid in Quarry Tunnel in the down direction, where the display equalled anything we have seen on the frostiest of nights in an electrified third-rail area.

Today's rapidly developing third rail (at least in some states) is supporting driver's licenses for illegal immigrants, as favored by New York Gov. Eliot Spitzer.